1. Field of the Invention
Example embodiments of the present invention generally relate to shock tube devices and, more particularly, to shock tube devices that generate multiple, e.g., primary and secondary, shock waves.
2. Description of the Related Art
Shock tube assemblies are used to simulate static and dynamic pressure conditions resulting from large energy blasts. These large energy blasts may be the result of conventional explosive detonation or nuclear detonation, for example. By simulating the conditions of such blasts without an actual full scale detonation, it is possible to evaluate the effects of such blasts on various types of equipment ranging from relatively small test articles, such radios, to relatively large test articles, such as full-size operational shelters, vehicles, tanks and aircraft. In effect, the shock tube assembly is a specialized short duration wind tunnel used for test and evaluation of various structures. Typically, a shock tube assembly includes various sections, such as a driver section containing a pressurized gas which is ultimately used to create the shock wave, a diaphragm section to suddenly release the driver gas, an expansion nozzle section to port the driver gas into a test chamber, along with associated gas processing and support equipment. The test article to be tested is placed in the test section. The driver is normally a hollow cylindrical pressure vessel with one end closed and sealed at the other end by the diaphragm section and capable of holding room temperature or elevated temperature gas at substantial pressure. The diaphragm section, associated with the driver, includes one or more diaphragms which are ruptured to release the gas in the driver, i.e., the shock tube diaphragm is mechanically, explosively or pressure ruptured to suddenly release the gas from the driver. In a dual diaphragm system, only one diaphragm is ruptured and the higher pressure differential imposed on the second diaphragm bursts it to release the gas. From the diaphragm section, the gas flows through the expander nozzle section, the discharge end of which is located within the expansion tube. The gas flowing through the nozzle section is supersonically expanded within the expansion chamber to create a shock wave which travels down the elongated expansion tube, compressing the air behind the travelling shock wave interface thereby providing both the static and dynamic pressure conditions and temperature conditions for testing and evaluating the test article located within the expansion tube and which is exposed to the static and dynamic pressure generated by the shockwave.
As mentioned above, the structure of classical and currently utilized blast tube is composed of a high pressure tubular section and a low pressure tubular section separated by a diaphragm. A diaphragm is a device, typically surface, that can change from a first state to a second state. In the first state, or closed state, the diaphragm acts as a barrier between the high pressure tubular section and the low pressure tubular section. In the second state, or open state, the diaphragm allows mixing between the high pressure tubular section and the low pressure tubular section.
The effectiveness of the shockwave is dependent on how rapidly and completely the designed system can switch from an open state to a closed state. The quicker that the diaphragm can switch to an open state is directly correlated to the characteristics and reproducibility of a shockwave.
Current, compressed-air driven blast tubes usually use one or two single or double diaphragms, which are placed between the high pressure and low pressure sections. In this configuration, blast tubes are only capable of generating single shock waves. Current blast tubes are not capable of reproducing multiple shock waves nor are they able to modify blast wave characteristics such as shape, duration, or peak.
Another type of blast tube system that is currently in operation utilizes explosives to generate blast waves. The choice and availability of explosives is a significant limit when it comes to broader research applications. Blast tube systems that utilize explosives for shock wave generation need complex and sophisticated control systems. These types of shock tubes also are subject to stringent safety measures.
There are several blast tubes, such as the ones at the University of Central Florida, City College of New York, and the Aerospace Corporation in EI Segundo, Calif., but these existing shock tubes are only able to reproduce non-ideal blast conditions. More particularly, existing blast tubes lack the ability to replicate multiple shock waves.
Operation of one type of conventional blast tube system will now be described with reference to FIGS. 1-2.
FIG. 1 illustrates a conventional blast tube system 100.
As illustrated in the figure, system 100 includes a tube section 102, a tube section 104, a test chamber 106, a diaphragm 108, a diaphragm 110, a detector 112, an inlet valve 114, an inlet valve 116, an outlet valve 118, an outlet valve 120, a compressor 122 and a controller 124.
Tube section 102 has an end wall 126 and an open end 128. Tube section 104 has an open end 130 and another open end 132. Test chamber 106 has an open end 134 and an end 136 that can be open or closed. Test chamber 106 contains detector 112 positioned at end 136.
Tube section 102 is arranged such that open end 128 is adjacent to open end 130 of tube section 104. Further, test chamber 106 is arranged such that open end 134 is adjacent to open end 132 of tube section 104. Detector 112 is disposed at closed end 136 of test chamber 106.
Compressor 122 is arranged to receive compressor control signal 138 from controller 124.
Inlet valve 114 is arranged to receive a fluid through fluid line 148 from compressor 122. Additionally, inlet valve 114 is arranged to receive inlet valve control signal 140 from controller 124. Inlet valve 116 is arranged to receive a fluid through fluid line 150 from compressor 122. Additionally, inlet valve 116 is arranged to receive inlet valve control signal 142 from controller 124. Outlet valve 118 is arranged to receive outlet valve control signal 144 from controller 124. Outlet valve 120 is arranged to receive outlet valve control signal 146 from controller 124.
Tube section 102 and tube section 104 are able to receive and store a fluid at a predetermined temperature, pressure, and volume. Tube section 102 and tube section 104 may be any known device or system that is able to receive and store a fluid at a predetermined temperature, pressure, and volume. Non-limiting examples of tube section 102 and tube section 104 include pipes, drums and containers.
Test chamber 106 is able to contain a shockwave and expansion of fluid created in tube section 102 and tube section 104. Test chamber 106 may be any known device or system that will allow the expansion of a fluid to propagate through itself. Non-limiting examples of test chamber 106 include a closed pipe, open end pipe and chamber.
Diaphragm 108 acts as a controllable barrier between tube section 102 and tube section 104. In a first state, or closed state, diaphragm 108 prevents the mixing of fluids from tube section 102 and tube section 104. In a second state, or open state, diaphragm 108 is open and allows the flow of fluid from tube section 102 into tube section 104, creating a primary shockwave.
Diaphragm 110 acts as a controllable barrier between tube section 104 and test chamber 106. In a first state, or closed state, diaphragm 110 prevents the passage of fluid from tube section 104 into test chamber 106. In a second state, or open state, diaphragm 110 is open and allows a shock wave and fluid from tube section 102 and tube section 104 to propagate into test chamber 106.
Diaphragm 108 and diaphragm 110 may be any known devices or system that is operable to be closed in a first state and open in a second state. Non-limiting examples of diaphragm 108 and diaphragm 110 include a thin membrane, valve and scored plate.
Detector 112 detects the pressure inside of test chamber 106. Detector 112 may be any known device or system that is able to detect pressure inside of test chamber 106. Non-limiting examples of detector 112 include a barometer and a piezoelectric sensor.
Inlet valve 114 allows fluid to flow from compressor 122, by way of fluid line 148, into tube section 102. Inlet valve 114 is controlled by controller 124 through inlet valve control signal 140. Inlet valve 116 allows fluid to flow from compressor 122, by way of fluid line 150, into tube section 104. Inlet valve 116 is controlled by controller 124 through inlet valve control signal 142.
Inlet valve 114 and inlet valve 116 may be any known device or system that allows unidirectional fluid flow from compressor 122. Non-limiting examples of inlet valve 114 and inlet valve 116 include a globe valve, gate valve or needle valve.
Outlet valve 118 allows the flow of fluid out of tube section 102. Outlet valve 118 is controlled by controller 124 by outlet valve control signal 144. Outlet valve 120 allows the flow of fluid out of tube section 104. Outlet valve 120 is controlled by controller 124 through outlet valve control signal 146.
Outlet valve 118 and outlet valve 120 may be any known device or system that allows unidirectional fluid flow from tube section 102 and tube section 104. Non-limiting examples of outlet valve 118 and outlet valve 120 include a globe valve, gate valve and needle valve.
Compressor 122 provides a fluid under a controlled flow rate and/or pressure to inlet valve 114. Additionally, compressor 122 provides a fluid under a controlled flow rate and/or pressure to inlet valve 116. Compressor 122 IS controlled by controller 124 through compressor control signal 138.
Compressor 122 may be any known device or system that is able to provide a fluid under a controlled flow rate and/or pressure to inlet valve 114 and inlet valve 116. Non-limiting examples of compressor 122 include a centrifugal compressor, mixed flow compressor or axial flow compressor.
Controller 124 may be any known device or system that is able to control compressor 122, inlet valve 114, inlet valve 116, outlet valve 118, outlet valve 120, and detector 112. Non-limiting examples of controller 124 include a computer and a server.
In operation, system 100 is used to generate a controlled blast for study. Initial parameters are set for a particular test. The starting temperature and pressure in each of tube section 102 and tube section 104 are predetermined in order to study a resulting blast. To achieve the starting temperature and pressure, a user inputs the associated predetermined fluid temperature, pressure and volume into controller 124 through a user interface (not shown). With temperature, pressure, and volume known, controller 124 can send compressor control signal 138 to compressor 122. Compressor control signal 138 will instruct compressor 122 to begin pumping fluid into tube section 102 and tube section 104.
Fluid is pumped at a predetermined flow rate and/or pressure to inlet valve 114 and inlet valve 116. Fluid is unable to pass through inlet valve 114 and inlet valve 116 until they are opened by controller 124, via inlet valve control signal 148 and inlet valve control signal 150.
Once inlet valve 114 and inlet valve 116 are open, fluid is pumped into tube section 102 and tube section 104, by compressor 122. When controller 124 has calculated that the amounts of fluid in tube section 102 and tube section 104 have reached the predetermined temperature, pressure, and volume limits, it sends compressor control signal 138 to indicate compressor 122 should shut down.
Simultaneously, controller 124 sends inlet valve control signal 148 to inlet valve 114 and inlet valve control signal 150 to inlet valve 116 indicating that they should close to prevent the flow of fluid into tube section 102 and tube section 104.
Once fluid in tube section 102 and tube section 104 reaches a predetermined temperature, pressure, and volume, a user may enter time variables into controller 124 through a user interface. In some embodiments, time variables may be preset. The time variables are used to control the opening of diaphragm 108 and diaphragm 110.
There are several methods of opening a diaphragm in a blast tube system. One example method of opening a diaphragm is to have the diaphragm electrically actuated. In this method when the diaphragm receives a signal, it will open through electro-mechanical means. Another example method of opening a diaphragm is to have a diaphragm with a set pressure tolerance, and when the pressure tolerance is exceeded, the diaphragm ruptures allowing fluid to flow from tube section 102 to tube section 104. Another example method of opening a diaphragm is to have a diaphragm with a set temperature tolerance, and when the temperature tolerance is exceeded, the diaphragm ruptures allowing fluid to flow from tube section 102 into tube section 104.
Any of the above mentioned diaphragm control methods may be used individually or in conjunction with one another to achieve precise diaphragm timing.
For purposes of discussion, in this example embodiment, diaphragm 108 is electrically actuated, wherein control signal 152 will provide a voltage as to open diaphragm 108. Also in this example embodiment, diaphragm 110 is electrically actuated, wherein control signal 154 will provide a voltage as to open diaphragm 110.
At time t1, controller 124 will send diaphragm control signal 152 to diaphragm 108 indicating that it should switch from a closed state to an open state. When diaphragm 108 is switched to an open state, the temperature and pressure differential between tube section 102 and tube section 104 will facilitate the generation of a shockwave. The resultant shockwave will propagate from tube section 102 and tube section 104 towards test chamber 106.
At time t2, controller 124 will send diaphragm control signal 154 to diaphragm 110 indicating that it should switch from a closed state to an open state. This state change will allow the shockwave to propagate into test chamber 106. When the shock wave reaches test chamber 106, detector 112 will measure the pressure and temperature differentials that are created.
The detector will continue to measure temperature and pressure inside of test chamber 106 until the fluid reaches a state of equilibrium. Once the fluid has reached a state of equilibrium controller 124 will send outlet valve control signal 144 to outlet valve 118 and outlet valve control signal 146 to outlet valve 120. This will indicate that outlet valve 118 and outlet valve 120 should switch from a closed state to an open state. When outlet valve 118 and outlet valve 120 are open, fluid can be vented out of shock tube system 100.
FIG. 2 is a graph that illustrates the pressure at detector 112 inside of the shock tube system 100 described in FIG. 1 as a function of time.
As illustrated in FIG. 2, graph 200 includes a y-axis 202, an x-axis 204, and a function 206. Function 206 includes a function segment 208, a function segment 210, and a function segment 212. Y-axis 202 is pressure measured by detector 112 in Torr, whereas x-axis 204 is time in milliseconds.
Function segment 208 has a constant pressure p0 from time t0 to time t1. Function segment 210 has a maximum pressure p1 from time t1 to time t2. Function segment 212 decreases from pressure p1 to pressure p0 from time t2 to time t3.
In operation, at time t0 diaphragm 108 is in a closed state and acts as a barrier between tube section 102 and tube section 104. Additionally at time t0, diaphragm 110 is in a closed state and acts as a barrier between tube section 104 and test chamber 106. When tube section 102, tube section 104, and test chamber 106, are separated by diaphragm 108 and diaphragm 110, the pressure inside of shock tube system 100 is at a constant p0 as shown by function segment 208.
Function segment 210 represents the opening of diaphragm 108 at time t1. At time t1, diaphragm 108 switches from a closed state to an open state, allowing the flow of fluid from tube section 102 into tube section 104. The volume, temperature, and pressure differentials between tube section 102 and tube section 104 creates a primary shock with pressure p1.
The primary shock propagates from tube section 102 and tube section 104 towards test chamber 106 at a constant pressure p1 from time t1 to time t2.
At time t2, diaphragm 110 switches from a closed state to an open state allowing the primary shock to propagate into test chamber 106. When the primary shock enters test chamber 106, it begins to expand as the fluids begin to reach equilibrium in shock tube system 100.
Function segment 212 represents the expansion of the primary shock inside of test chamber 106. At time t2 the primary shock enters test chamber 106 and begins to equalize. This equalization continues until the fluid in test chamber 106 equalizes to a pressure higher than p0 at time t3.
Enhanced blast weaponry such as thermobaric bombs and nuclear devices create shockwaves with multiple shock wavefronts as well as multiple expansion wavefronts. Since conventional shock tubes are only able to create single wavefronts they are not suitable for biomedical research on enhanced blast weaponry injuries and damage mitigation, for example.
What is therefore needed is a system and method that generates a primary and secondary shockwave. Moreover, a system that creates multiple shockwaves will provide researchers with additional fundamental understanding of how multiple shock wavefronts work. With better knowledge of how multiple shock wavefronts work, researchers will, for example, be able to develop methods for injury prediction, injury treatment, and damage mitigation.